The present invention relates, generally, to techniques for depositing conductive material onto a workpiece, such as a semiconductor wafer. More particularly, the invention relates to an apparatus, a system, and a method for both electrolytically depositing the conductive material onto the workpiece surface and polishing the surface of the workpiece to remove a portion of the conductive material.
Microelectronic circuits generally include conductive features such as via plugs, metal lines, and the like to interconnect various portions or layers of the circuit. The conductive features of the microelectronic circuits include conductive material such as metal and often include a barrier material to reduce unwanted diffusion of the conductive material and promote adhesion between the conductive material and an adjacent layer of the circuit.
Aluminum is often used to form conductive features because aluminum features are relatively easy to manufacture using conventional deposition (e.g., chemical vapor deposition) and etch (e.g., reactive ion etch) techniques. While use of aluminum to form conductive features is adequate for some circuits, the use of aluminum to form conductive features becomes increasingly problematic as the size of the conductive feature decreases. In particular, as the size of the conductive feature decreases, the current density through the feature generally increases and thus the feature becomes increasingly susceptible to electromigration, i.e., the mass transport of metal due to the current flow. Electromigration may cause short circuits where the metal accumulates, opens where the metal has been depleted, or other circuit failures. Similarly, increased conductive feature resistance may cause unwanted device problems such as excess power consumption or heat generation.
Recently, techniques have been developed to form conductive features comprising copper, which is less susceptible to electromigration and which exhibits a lower resistivity than aluminum. Because copper does not readily form volatile or soluble compounds, the copper conductive features are often formed using damascene technology. More particularly, the copper conductive features are formed by creating a via within an insulating material, blanket depositing a barrier layer onto the surface of the insulating material and into the via, blanket depositing a seed layer of copper onto the barrier layer, electrodepositing a copper layer onto the seed layer to fill the via, and removing any excess barrier material and copper from the surface of the insulating material using chemical mechanical polishing. During the eletrodeposition process, additives such as leveling agents are continuously or regularly added to the plating bath to reduce formation of voids within the conductive features. Such leveling agents may affect the grain boundaries of the deposited material, necessitating a subsequent anneal process to obtain the desired material properties.
Forming copper conductive features according to the method described above can be relatively expensive, in part, because each material deposition and removal step is typically carried out using dedicated equipment. U.S. Pat. No. 6,176,922, issued to Talieh on Jan. 23, 2001 discloses an apparatus for both electroplating copper and polishing the copper. The apparatus disclosed in Talieh includes a wafer carrier having a cathode electrode contact, which contacts the surface of the wafer to be polished. The apparatus disclosed in Talieh may be problematic in several regards. In particular, a film deposited using the apparatus of Talieh may be undesirably non-uniform because the cathode electrode contacts the wafer in a limited number of fixed locations about a perimeter of the wafer. Such a cathode contact configuration may lead to increased deposition about the perimeter of the wafer (in the areas proximate the cathode contact) and thus lead to non-uniform deposition of the conductive film. Furthermore, wafer areas in contact with the cathode generally cannot include active devices. Accordingly, improved methods and apparatus for electrochemically depositing a film and for polishing the film are desired.
The present invention provides improved apparatus and methods for forming conductive features on a surface of a workpiece. More particularly, the invention provides an improved apparatus capable of both depositing material onto a surface of a workpiece and polishing the workpiece surface and a method of forming conductive features using the apparatus. While the ways in which the invention addresses the drawbacks of the now-known deposition and polishing apparatus are addressed in greater detail below, in general, the apparatus in accordance with the present invention provides a cathode contact embedded in a polishing surface, such that the workpiece can move relative to the cathode contact during material deposition.
In accordance with an exemplary embodiment of the present invention, an electrochemical deposition apparatus includes a polishing platen having a polishing surface and a tank including an electrolyte solution. Electrodeposition results when a sufficient bias is applied between the platen and a workpiece surface, which is in contact with the solution. In accordance with one aspect of this embodiment, a potential is applied to the workpiece surface using connectors embedded within the polishing surface and electrically insulated from the platen. Because the workpiece receives a potential from connectors embedded within the polishing surface, rather than from a wafer carrier, more workpiece surface is available for conductive feature formation and potentially more uniform films may be deposited.
In accordance with a further embodiment of the invention, the polishing surface includes a polishing pad attached to the platen to facilitate removal of conductive material from the surface of the workpiece. In accordance with one aspect of the invention, the polishing pad includes apertures to allow a portion of the connectors to contact the surface of the workpiece. The pad may also include channels for electrolyte solution flow and groves on the surface of the polishing pad to facilitate mass transport of the solution to and from the workpiece surface.
In accordance with yet a further embodiment of the invention, the apparatus includes a temperature control device and a chiller to cool solution applied to the workpiece surface.
In accordance with an alternative embodiment of the invention, a workpiece carrier includes a heat exchanger.
In accordance with yet another embodiment of the invention, a polishing platen includes a heat exchanger.
In accordance with yet a further embodiment of the present invention, the electrochemical planarization apparatus includes an endpoint detection apparatus configured to detect an endpoint of a deposition and planarization process of a workpiece.
In accordance with a further embodiment of the invention, a conductive feature is formed on a surface of a workpiece by placing a workpiece surface in contact with a polishing surface having electrical conductors embedded therein and applying a bias between the workpiece and a polishing platen in the presence of an electrolyte. In accordance with one aspect of this embodiment, the workpiece and the polishing surface move relative to each other during the deposition process.